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Bomb Lab Phase 1|Hợp ngữ và mã máy
Bomb Lab Phase 1|Hợp ngữ và mã máy


Binary Bomb Lab :: Phase 1

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  • Summary of article content: Articles about Binary Bomb Lab :: Phase 1 Learn how to work through Phase 1 of Bryant and O’Hallaron’s Binary Bomb lab step by step. Get started on the path to defeating Dr. Evil! …
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Binary Bomb Lab :: Phase 1
Binary Bomb Lab :: Phase 1

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Cách  Giải chung của các  bomb nhị phân (binary) từ phase 1 -2

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  • Summary of article content: Articles about Cách  Giải chung của các  bomb nhị phân (binary) từ phase 1 -2 csapp/Lab2 [Bomb Lab]/bombs/bomb1.tar · 46ff9e86e3cdfe9979ce32398313d4be8d2f6b56 · Alka / computer_ · GitLab. git.lug.ustc.edu.cn. …
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Cách  Giải chung của các  bomb nhị phân (binary) từ phase 1 -2
Cách  Giải chung của các  bomb nhị phân (binary) từ phase 1 -2

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GitHub – sc2225/Bomb-Lab: Guide and work-through for System I’s Bomb Lab at DePaul University. (**Please feel free to fork or star if helpful!)

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  • Summary of article content: Articles about GitHub – sc2225/Bomb-Lab: Guide and work-through for System I’s Bomb Lab at DePaul University. (**Please feel free to fork or star if helpful!) Bomb-Lab. DePaul University – System I – Winter 2017. **Note: I made this repo with the intent to help others solve their own Bomb Labs. …
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GitHub - sc2225/Bomb-Lab: Guide and work-through for System I's Bomb Lab at DePaul University. (**Please feel free to fork or star if helpful!)
GitHub – sc2225/Bomb-Lab: Guide and work-through for System I’s Bomb Lab at DePaul University. (**Please feel free to fork or star if helpful!)

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CS3330: Bomb Lab

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Contents

Submission

Viewing your results

About Collaboration

Getting a bombs from ssh

Basic Strategy

Bomb Usage

Examining the Executable

Using GDB

On interpreting the disassembly

CS 3330 Fall 2018

CS3330: Bomb Lab
CS3330: Bomb Lab

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Nhờ giải bài tập Binary Bomb Lab môn kiến trúc máy tính – programming – Dạy Nhau Học

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Nhờ giải bài tập Binary Bomb Lab môn kiến trúc máy tính - programming - Dạy Nhau Học
Nhờ giải bài tập Binary Bomb Lab môn kiến trúc máy tính – programming – Dạy Nhau Học

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bomb lab

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  • Summary of article content: Articles about bomb lab What is Bomb Lab? •An exercise in reading x86-64 assembly code. •A chance to practice using GDB (a debugger). •Why? • x86 assembly is low level machine code … …
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bomb lab

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Binary Bomb Lab :: Phase 1

A note to the reader: For explanation on how to set up the lab environment see the “Introduction” section of the post.

If you’re looking for a specific phase:

Phase 1 is sort of the “Hello World” of the Bomb Lab. You will have to run through the reverse engineering process, but there won’t be much in the way of complicated assembly to decipher or tricky mental hoops to jump through. To begin, let’s take a look at the function in our objdump file:

The function is rather simple. It moves some things around, and then pushes two values onto the stack before calling the function on them. One of these values is stored in the register %eax and the other appears to be stored in the code at $0x80497c0 . If we really wanted to be pedantic, we could go check out what does, but I think it’s pretty safe to assume that it checks equality of the strings.

Moving on: if the strings are equal, the function runs to jump over the function. So, what does do in a nutshell? It takes your standard input, stores it in %eax , and then compares it to the string at $0x80497c0 . If they’re equal, you get to go to the next phase.

Given that the string we’re looking for is stored at a fixed memory address, we know that it must have printed out somewhere within our strings output text file. Unfortunately, it could be any of those strings for all we know. We will have to use gdb to find out a little more.

First things first, let’s fire up gdb and set a breakpoint on the function. This will ensure that the bomb doesn’t blow up when we run the program with the compiler. Set the breakpoint with the command break phase_1 . Next, run the program with the run command.

As you can see in the screenshot above, once you run the program, “Dr. Evil” (stdin) asks you for the first password. Let’s enter the string “test string”, since we know our breakpoint will save us from bomb detonation. As soon as we enter our string and press enter, the breakpoint stops execution of the program. Now we can take a look at the values in our two memory addresses of interest, $eax and the fixed address 0x80497c0 . We will use the gdb command x , and ask for the 25 characters that follow the memory address. Since the register $eax is not a fixed memory address, we’ll have to first use p/x to find its address. p/x $eax quickly lets us know that the currently allocated address for the register is 0x804b680 .

At this point, all we have to do is check the contents of each memory address. As expected, running x /25c 0x804b680 gives us our inputted string “test string” . When we run the command on the fixed address, x /25c 0x80497c0 , we get something exciting! The 25 characters that follow the memory address are “Public speaking is very e” . Let’s head to our strings output to check for a string that starts this way:

There it is, plain as day! The answer to Phase 1 is the string “Public speaking is very easy.” Let’s input it into our bomb to make sure:

Hooray! On to Phase 2.

CS3330: Bomb Lab

Introduction

A Mad Programmer got really mad and planted a slew of “binary bombs” on our class machines. A binary bomb is a program that consists of a sequence of phases. Each phase expects you to type a particular string on stdin . If you type the correct string, then the phase is defused and the bomb proceeds to the next phase. Otherwise, the bomb explodes by printing “BOOM!!!” and then terminating. The bomb is defused when every phase has been defused.

There are too many bombs for us to deal with, so we are giving each student a bomb to defuse. Your mission is to defuse your bomb before the due date. Good luck, and welcome to the bomb squad!

Your task

Obtain a “binary bomb” as described below. Note that this program will automatically communicate with our server. This is how you will be graded. If your bomb “explodes”, it will notify our server. Too many explosions will lose you points.

The bomb program will ask you you for a secret input.

Defuse the “phases” of the bomb by figuring out (e.g. using a debugger) what the secret input for each “phase” is. (You will not get credit for using the debugger to jump over the code that checks whether input is valid; the bomb must send a correct input to our server.)

For lab : defuse phase 1. You will get full credit for defusing phase 1 with less than 20 explosions. There is a small grade penalty for explosions beyond 20.

: defuse phase 1. For homework : defuse phases 2 and 3. You will get full credit for defusing phases 2 and 3 with less than 30 explosions. There is a small amount of extra credit for each additional phase defused. There is a small grade penalty for explosions beyond 30.

: defuse phases 2 and 3.

Submission

There is no explicit submission. The bomb will notify your instructor automatically about your progress as you work on it.

Viewing your results

You can see your grade, updated with about a 1-hour delay on the gradebook.

There is scoreboard showing how many explosions and phases defused all bombs have here, which is updated more frequently.

About Collaboration

For phase 1, anything goes. Being a lab, you can work together as much as you want.

For phases 2 and beyond, it is homework so more restrictions apply. You are welcome to discuss with one another the process and tools you use, but please do not look at or describe one another’s code.

Obtaining your bomb

Use Linux. This lab only works on 64-bit Linux machines. The department Unix machines qualify; see these instructions if you need help accessing them remotely. You can obtain your bomb by pointing your Web browser at: http://archimedes.cs.virginia.edu:15213/ This will display a binary bomb request form for you to fill in. Enter your computing ID and email address and hit the Submit button. The server will build your bomb and return it to your browser in a tar file called bombk.tar , where k is the unique number of your bomb. Save the bombk.tar file to a (protected) directory in which you plan to do your work. Then give the command: tar -xvf bombk.tar . This will create a directory called ./bombk with the following files: README : Identifies the bomb and its owners.

: Identifies the bomb and its owners. bomb : The executable binary bomb.

: The executable binary bomb. bomb.c : Source file with the bomb’s main routine and a mad greeting from the Mad Mad Programmer. If for some reason you request multiple bombs, this is not a problem. Choose one bomb to work on and delete the rest.

Getting a bombs from ssh

If you are trying to do the lab without a browser on the machine being used, try the following:

curl “http://archimedes.cs.virginia.edu:15213/?username= $USER &usermail= $USER @virginia.edu&submit=Submit” > bomb.tar mv bomb.tar $( head -1 bomb.tar | cut -d ‘/’ -f1 ) .tar

Note, this might fail if the remote machine you run it on is not a department machine because $USER might not be set correctly by other machines. Replace $USER with your computing ID if you are running this command e.g. in cloud9, koding, or codio.

Hints

Basic Strategy

The best way is to use your favorite debugger to step through the disassembled binary. Almost no students succeed without using a debugger like gdb or lldb. On the department Unix machines, gdb is the debugger that is available. By default GDB verison 7.3 is available, and you can use GDB version 8 by running module load gdb-8.1 then running gdb .

Try running objdump -t bomb . This will show you the symbols in the executable, including the names of all methods. Look for one that looks dangerous, as well as some that looks like interesting methods (perhaps something like “Phase 1”).

To avoid accidentally detonating the bomb, you will need to learn how to single-step through the assembly code and how to set breakpoints. You will also need to learn how to inspect both the registers and the memory states.

It may be helpful to use various utilities for examining the bomb program outside a debugger, as described in “examining the executable” below.

Bomb Usage

The bomb ignores blank input lines.

If you run your bomb with a command line argument, for example, linux> ./bomb psol.txt then it will read the input lines from psol.txt until it reaches EOF (end of file), and then switch over to stdin . This will keep you from having re-type solutions.

Examining the Executable

objdump -t will print out the bomb’s symbol table. The symbol table includes the names of all functions and global variables in the bomb, the names of all the functions the bomb calls, and their addresses. You may learn something by looking at the function names!

objdump -d will disassemble all of the code in the bomb. You can also just look at individual functions. Reading the assembler code can tell you how the bomb works. If you prefer to get Intel syntax disassembly from objdump , you can use objdump -M intel -d .

strings is a utility which will display the printable strings in your bomb.

Using GDB

If you are on a department Unix machine, you might want to run module load gdb-8.1 first, so gdb is the most recent available version of GDB. (By default you will get GDB 7.3.)

Run bomb from a debugger like gdb instead of running it directly. The debugger will allow you to stop the bomb before it detonates. For example, if I ran linux> gdb bomb (gdb) b methodName (gdb) run (gdb) kill this will start gdb , set a breakpoint at methodName , and run the code. The code will halt before it runs methodName ; calling kill will stop the bomb and exit the current debugging session without methodName running.

Use “step” and “stepi” to examine this function. “step” runs your code one line of source code at a time. “stepi” runs your code one line of machine instruction at a time. This allows you to run “phase_1()” piece by piece.

Use this to step carefully through phase_1() to see if you can find the passphrase. linux> gdb bomb (gdb) b lineNumberForPhase1Call (gdb) run input test passphrase here (gdb) stepi (gdb) info locals (gdb) info registers Generally some parameters are local variables and some are stored in registers. You should see your test passphrase here. Note the hex value of your input (gdb) stepi If you want to see the assembly code you’re stepping through, use “disas methodNmae”. keep stepi ing until you see strings_not_equal method (a suspicious name that might be checking your passphrase) (gdb) info locals (gdb) info registers Which one holds your passphase? Try “examining” that and others…

Some useful gdb commands: (gdb) info locals prints out the name and value of local variables in scope at your current place in the code. (gdb) info registers prints the values of all registers except floating-point and vector registers (gdb) x/20bx 0x… examine the values of the 20 bytes of memory stored at the specified memory address (0x…). Displays it in hexadecimal bytes. (gdb) x/20bd 0x… examine the values of the 20 bytes of memory stored at the specified memory address (0x…). Displays it in decimal bytes. (gdb) x/gx 0x… examine the value of the 8-byte integer stored at the specified memory address. (gdb) x/s 0x… examines the value stored at the specified memory address. Displays the value as a string. (gdb) x/s $someRegister examines the value at register someRegister. Displays the value as a string (assuming the register contains a pointer). (gdb) print expr evaluates and prints the value of the given expression call (void) puts (0x…) calls the built-in output method puts with the given char * (as a memory address). See man puts for more. (gdb) disas methodName gives you the to get the machine instruction translation of the method methodName . (gdb) disas gives you the to get the machine instruction translation of the currently executing method. (gdb) x/6i 0x… try to disassemble 6 instructions in memory starting at the memory address 0x… (gdb) set disassembly-flavor intel switches GDB to Intel syntax disassembly (the syntax you used in 2150; not the syntax we will use for the rest of the course) (gdb) set disassembly-flavor att switches GDB back to AT&T syntax disassembly, the default and the syntax we will use for the rest of the course (gdb) b *0x… set a breakpoint at the specified memory address (0x…). (gdb) b function_name. set a breakpoint at the beginning of the specificed function. (gdb) nexti step forward by one instruction, skipping any called function. (gdb) kill termiante the program immediately (gdb) help brings up gdb’s built-in help menu The textbook also has a nice summary of useful gdb commands on page 280 (or 255 of the 2nd edition). You can also find sources like http://csapp.cs.cmu.edu/2e/docs/gdbnotes-x86-64.txt that list and describe other useful gdb commands.

On interpreting the disassembly

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